Scroll compressors have orbital scrolls which are driven in a generally circular orbit. These orbital scrolls include a plate with a flat surface that is perpendicular to an orbit axis and an involute wrap integral with the plate and extending out from the flat surface. A non-rotatable scroll including a plate with a flat surface that is parallel to the flat surface of the orbital scroll and an involute wrap integral with the plate and extending out from the flat surface cooperates with the orbital scroll to form at least a pair of fluid pockets. The fluid pockets are bound by adjacent surfaces of the wraps, line contacts between the wraps and contact between the axial tips of the wraps and the flat surface of the adjacent scroll. A seal is normally provided in a groove in the axial tips of each scroll wrap to seal between the wrap and the flat surface of the adjacent scroll. Axial tip seals are provided to accommodate thermal expansion of the scroll end plates and the scroll wraps.
The orbital scroll is driven to cause the contact lines between the wraps to move along the surface of the wraps toward the center of the scrolls. As the contact lines move, the fluid pockets move toward the center of the scrolls, the pockets become smaller and the fluid in the pockets is compressed. A fluid outlet aperture is provided in the center portion of one of the scrolls.
The compressed fluid in the scroll pockets exerts an axial force on the parallel flat surfaces of the scroll end plates. This force tends to separate the scrolls and cause leakage of compressed fluid between the axial edges of the scroll wraps and the flat surface of the adjacent scroll. The force of compressed fluid also tends to distort the scroll end plates with flat surfaces. The distortion results from the fact that the radial outer edges of the scroll plates are at compressor inlet pressure and the center of the scrolls is at the higher compressor outlet pressure.
Scroll type compressors with a fixed scroll and an orbital scroll are known which hold the orbital scroll in a fixed axial position relative to the axis about which the scroll orbits. The fixed scroll is then subjected to an axial thrust load which moves the fixed scroll toward the orbital scroll.
The orbital scroll is held from rotation and allowed to move in an orbit. The drive means for moving the orbital scroll in an orbit includes a crankshaft. The crankshaft can drive the orbital scroll through a direct connection or it can be connected to the orbital. scroll through a pivoting link or a sliding link that permits some variation in the radius of the scroll orbit. It is desirable to allow some change in the radius of the orbit to keep the scroll wraps in contact with each other, to accommodate normal manufacturing tolerances and to prevent damage to the scroll wraps due to solids mixed with the fluid.
The orbital scroll and scroll drive require balancing to reduce vibration. Balance weights are connected to the crankshaft or in some cases to the links that connect the crankshaft to the orbital scroll.
The inertial forces on a scroll compressor tend to cock the orbital scroll. If the orbital scroll cocks so that its end plate is not parallel to the fixed scroll end plate, scroll efficiency can be reduced and the rate of scroll wear can be increased. The orbital scroll can be held in position by increasing the axial loads on the scrolls, by employing connections between the scroll drive and the orbital scroll which tend to hold the orbital scroll in proper alignment with the fixed scroll and by careful placement of balance weights. The design employed to maintain scroll alignment must be consistent with size, weight and cost considerations.